With an initiative to legalize marijuana in California likely heading to the November ballot, medical providers, health care experts and industry groups are sharply divided over the controversial measure.

It is already legal in California to use cannabis with a doctor’s prescription. The Adult Use of Marijuana Act would allow adults 21 years and older to possess up to one ounce of it and grow up to six plants for non-medical use. The initiative also would impose a 15 percent tax on recreational marijuana sales.

California would follow Colorado, Washington, Alaska and Oregon in allowing the recreational use of marijuana if the measure is approved. Proponents say they have collected the required number of signatures to qualify for the November ballot. State officials are verifying those signatures, and the measure could be approved for the ballot within the next two weeks.

Other health experts remain concerned about the health effects of legalizing marijuana for adults, even as they acknowledge some benefits of the initiative.

“There is some good stuff in the initiative,” said Rachel Barry, a researcher at the University of California, San Francisco. But the measure lacks sufficient protection for public health, she said.

Barry coauthored an analysis of the ballot measure, which concluded that the toxicity of marijuana smoke is similar to that of tobacco. This includes the harm caused by secondhand smoke.

A more fitting ballot initiative, according to Barry’s report, would be one that treated marijuana in the same way as tobacco — legal but undesirable.

“This initiative does not accomplish the goal that would prevent a public health catastrophe, because it doesn’t focus on prevention strategies,” Barry said. And the priority of the marijuana industry will be to make money by increasing consumption, she added.

Supporters say marijuana legalization and regulation is a proven success in other states. They point to millions of dollars in tax revenue for state and local governments. But opponents say it depends on whom you ask.

“What we have found from the Colorado experience is that there are more patients in the emergency rooms,” said Bill Emmerson, vice president of government relations for the California Hospital Association. “We already see [overcrowding] in our emergency rooms as a result of the Affordable Care Act and mental health issues.”

The current initiative fails to take into account the burden on hospitals, Emmerson added.

A study by Northwestern Medicine and the University of Colorado School of Medicine, published earlier this year, found a spike in Colorado emergency room visits by out-of-state visitors.

Marijuana-related visits to the emergency room by non-residents more than doubled between 2012 — when recreational marijuana was first legalized in Colorado — and 2014.

The medical community’s views on marijuana have evolved over the years.

The California Medical Association called the measure “comprehensive” and said that while it does not encourage the use of marijuana, controlling and regulating it is the most effective way to protect public health.

“The perception has changed,” said Donald Lyman, a retired physician and chair of the group’s Council on Science and Public Health. “We know it is not a useless substance; there are medical uses and it is time to look at the regulatory system.”

“Because it is a legitimate product, there should be a legitimate access point,” Lyman argued.

How the availability of recreational marijuana might affect California’s medical marijuana industry remains to be seen. It’s possible that marijuana for medical reasons might be discounted, although the measure does not address that. But if pricing for recreational marijuana is similar to that of medical marijuana, the medical cannabis industry may eventually disappear, Lyman said. That’s something that market forces will decide, he said.

“The CMA did not support the initiative with the intent to drive [the medical cannabis industry] out,” Lyman said. “But if that were the case, most physicians would not be unhappy.”

He said physicians often find themselves stuck in between state law, which allows for cannabis recommendations, and federal law, which says it’s illegal.

Last year, Gov. Jerry Brown signed a package of bills to regulate the 20-year-old medical marijuana industry. The new rules, which include licensing requirements, help doctors ensure that when they make a recommendation for medical cannabis their patients are getting a safe product, Lyman said.

The marijuana legalization measure appears to extend those rules to the recreational market. With similar rules for both recreational and medical marijuana, the state will be able to compete against the black market, Lyman said.

The CMA’s support of the Adult Use of Marijuana Act reflects its own evolving position on marijuana. In a 2011 policy statement, the organization said marijuana should be treated like alcohol and tobacco, and removed from the U.S. Drug Enforcement Agency’s list of drugs with no accepted medical use. Reclassifying cannabis would facilitate clinical research to evaluate its risks and benefits, the CMA said.

Dr. Barth Wilsey, an associate physician at UC San Diego’s Center for Medicinal Cannabis Research, said that just as alcohol prohibition ended during the Great Depression, it would not be surprising to see marijuana be legalized as the state and nation continue to climb out of the Great Recession. Governments want the tax revenues, he said, especially during times of economic distress.

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